This invention relates generally to polymer foams based upon a blend of an olefin polymer and at least one of an alpha-olefin (.alpha.-olefin)/vinyl monomer interpolymer and an .alpha.-olefin/vinylidene monomer interpolymer. The vinyl and vinylidene monomers may be aromatic, sterically hindered aliphatic, or cycloaliphatic. This invention relates particularly to open cell polymer foams based upon such blends, especially where the foams are soft and flexible and, preferably, of low density. This invention also relates to low density polymer foams (either open cell or closed cell) based upon such blends that more preferably have a skin that is smooth, aesthetically appealing and, still more preferably, functionally improved relative to foams prepared solely from an olefin polymer. These foams are preferably substantially free of cross-linking as evidenced by a low insoluble gel content.
A variety of thermoplastic polymers find their way into polymer foams. Certain thermoplastic polymers foam more readily than others do to provide structures with a variety of useful properties and dimensions. For example, polystyrene is an amorphous polymer that foams over a relatively broad range of temperatures, producing foams with a wide range of open-cell contents. On the other hand, semi-crystalline polymers typically foam over a narrow temperature range (relative to polystyrene) as their viscosities and melt strengths drop rapidly as temperatures exceed their respective crystalline melting points. This usually results in foams with a predominantly closed-cell configuration. One means of increasing melt strength of semi-crystalline polymers, thereby broadening the temperature range and improving a range of processing characteristics, involves lightly cross-linking the polymers by peroxides, irradiation or other conventional means. Even then, the resulting foams typically have a configuration that is predominantly closed-cell (less than 20 volume percent (vol %) open cell content).
Non-cross-linked, low-density olefinic polymer foams typically have rough skins upon manufacture. As the foams age, skin roughness may increase due to foams shrinkage or expansion. The rough skin lacks aesthetic appeal in many applications (e.g., cushion packaging). This leads to its removal at the time of final foam fabrication and results in wasted material.
PCT publication number WO/9810015 describes blends of polyolefins and .alpha.-olefin/vinylidene monomer interpolymers. Examples 26, 27 and 29-31 relate to foam materials prepared from such blends. Example 26 reports foam materials with a width of 32 millimeters (mm) and a thickness of either 15 mm or 17 mm. Example 27 has a width of 34.5 mm and a thickness of 19 mm. Examples 29-31 show closed cell foam preparation (less than (&lt;) 20 percent (%) open cell content), but do not report foam size.